Dielectric resonator having adjustment plates movable with respect to resonator disc and each other

ABSTRACT

A dielectric resonator including a dielectric resonator disc, a frequency controller including an adjustment mechanism and a dielectric adjustment plate, which is substantially parallel with the resonator disc, and movable means of the adjustment mechanism in the perpendicular direction with respect to the resonator disc for adjusting the resonance frequency. The frequency adjuster includes a plurality of dielectric adjustment plates, which are substantially installed concentrically and parallel one after another. The mechanical engagement of the plates with each other and with the adjustment mechanism enabling movement of the adjustment plates both with respect to the resonator disc and to each other, so that the adjustment plates are arranged in layers on top of each other as the adjusting movement is proceeding. This results in improved linearity of frequency control and a longer adjustment distance, which both improve the adjustment accuracy.

This application claims benefit of international applicationPCT/FI95/00545, filed Oct. 4. 1995.

BACKGROUND OF THE INVENTION

The invention relates to a dielectric resonator comprising a dielectricresonator disc, a frequency controller comprising an adjustmentmechanism and a dielectric adjustment plane, which is substantiallyparallel with the resonator disc, and movable by means of the adjustmentmechanism in the perpendicular direction with respect to the resonatordisc for adjusting the resonance frequency, and an electricallyconductive casing.

Recently, so-called dielectric resonators have become more and moreinteresting in high frequency and microwave range structures, as theyprovide the following advantages over conventional resonator structures:smaller circuit sizes, higher degree of integration, improvedperformance and lower manufacturing costs. Any object which has a simplegeometric shape, and the material of which exhibits low dielectriclosses and a high relative dielectric constant may function as adielectric resonator having a high Q value. For reasons related tomanufacturing technique, a dielectric resonator is usually of acylindrical shape, such as a cylindrical disc.

The structure and operation of dielectric resonators are disclosed e.g.in the following articles:

1! "Ceramic Resonators for Highly Stabile Oscillators", Gundolf Kuchler,Siemens Components XXIV (1989) No. 5, p. 180-183.

2! "Microwave Dielectric Resonators", S. Jerry Fiedziuszko, MicrowaveJournal, September 1986, p. 189-189.

3! "Cylindrical Dielectric Resonators and Their Applications in TEM LineMicrowave Circuits", Marian W. Pospieszalski, IEEE Transactions onMicrowave Theory and Techniques, VOL. MTT-27, NO. 3, March 1979, p.233-238.

The resonance frequency of a dielectric resonator is primarilydetermined by the dimensions of the resonator body. Another factor thathas an effect on the resonance frequency is the environment of theresonator. By bringing a metallic or some other conductive surface tothe vicinity of the resonator, it is possible to intentionally affectthe electric or magnetic field of the resonator, and thus the resonancefrequency. In a typical method for adjusting the resonance frequency ofthe resonator, the distance of a conductive metallic surface from theplanar surface of the resonator is adjusted. Alternatively, it is alsopossible to bring another dielectric body to the vicinity of theresonator body instead of a conductive adjustment body. One prior artfilter design of this kind, based on dielectric plate adjustment isshown in FIG. 1, in which a resonator comprises inductive coupling loops5 (input and output), a dielectric resonator disc 3 installed in a metalcasing 4, and supported by a dielectric leg 6, and a frequencycontroller attached to the metal casing 4, comprising an adjustmentscrew 1 and a dielectric adjustment plane 2. The resonance frequency ofthe resonator depends on the adjustment distance L in accordance with agraph shown in FIG. 2.

As appears from FIG. 2, the resonance frequency varies as a non-linearfunction of the adjusting distance. Due to this non-linearity and thesteep slope of adjustment, accurate adjustment of the resonancefrequency is difficult and demands great precision, particularly at theextreme ends of the control range. Frequency adjustment is based on ahighly accurate mechanical movement, the slope of adjustment k alsobeing steep. In principle, the length and thus the accuracy of theadjusting movement may be increased by reducing the size of the metallicor dielectric adjustment plane. Due to the non-linearity of theabove-mentioned adjusting techniques, however, the achieved advantage issmall, since the portion of the adjusting curve which is too steep ortoo flat either at the beginning or at the end of the adjusting movementcan not be used. When the resonance frequency becomes higher, e.g. tothe range 1500-2000 MHz or higher, the dimensions of the basic elementsof the dielectric filter, such as the dimensions of the resonator bodyor the adjustment mechanism are reduced even more. As a result,adjusting the resonance frequency of a dielectric resonator with priorart solutions sets very high demands on the frequency adjustmentmechanism, which, in turn, increases the material and production costs.In addition, as the mechanical movements of the frequency adjustmentdevice must be made very small, adjustment will be slower.

SUMMARY OF THE INVENTION

The object of the invention is a dielectric resonator providing a higheraccuracy and linearity of frequency control.

This is achieved with a dielectric resonator, which is characterized inaccordance with the invention in that the frequency controller comprisesa plurality of dielectric adjustment planes, which are substantiallyinstalled concentrically and parallel one after another, the mechanicalengagement of the planes to each other and to the adjustment mechanismenabling movement of the adjustment plates both with respect to theresonator disc and each other, so that the adjustment plates arearranged in layers on top of each other as the adjusting movement isproceeding.

In the invention, a conventional single dielectric adjustment plate hasbeen replaced with several thin dielectric adjustment plates, which canmove both with respect to each other and with respect to the resonatordisc, forming layers on top of the resonator disc as the adjustment isproceeding. The advantages of the invention are improved linearity offrequency adjustment, and a longer adjusting distance, which bothimprove the accuracy of adjustment.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be disclosed in greater detail byway of example with reference to the attached drawings, in which:

FIG. 1 shows a cross-sectional side view of a dielectric resonator inaccordance with the prior art,

FIG. 2 shows a graph illustrating the resonance frequency of theresonator shown in FIG. 1 as a function of the adjusting distance L,

FIGS. 3 and 4 show cross-sectional side views of a dielectric resonatorof the invention in two different adjusting positions, and

FIG. 5 shows a graph illustrating the resonance frequency of theresonator shown in FIGS. 3 and 4 as a function of the adjusting distanceL.

DETAILED DESCRIPTION

The structure, the operation and the ceramic manufacturing materials ofdielectric resonators are disclosed e.g. in the above-mentioned articles1!, 2!, and 3!, which are incorporated herein by reference. In thefollowing description, only the parts in the structure of the dielectricresonator which are essential to the invention will be disclosed.

The term dielectric resonator body, as used herein, generally refers toany object which has a suitable geometric shape, and the manufacturingmaterial of which exhibits low dielectric losses and a high relativedielectric constant. For reasons related to manufacturing technique, adielectric resonator is usually of a cylindrical shape, such as acylindrical disc. The most commonly used material is ceramic material.

The electromagnetic fields of a dielectric resonator extend beyond theresonator body, so it may easily be coupled electromagnetically to therest of the resonator circuit in a variety of ways depending on theapplication, e.g. by means of a microstrip conductor placed in thevicinity of the resonator, an inductive coupling loop, a bent coaxialcable, a straight wire, etc.

The resonator frequency of a dielectric resonator is primarilydetermined by the dimensions of the dielectric resonator body. Anotherfactor that has an effect on the resonance frequency is the environmentof the resonator. By bringing a metallic or any other conductivesurface, or alternatively another dielectric body, i.e. a so-calledadjustment body, to the vicinity of the resonator, it is possible tointentionally affect the electric or magnetic field of the resonator,and thus the resonance frequency.

FIGS. 3 and 4 show a dielectric resonator provided with a layer plateadjuster in accordance with the invention. The resonator comprises adielectric, preferably a cylindrical resonator disc 33 inside a casing34 made of electrically conductive material, such as metal, said discbeing preferably ceramic and placed at a fixed distance from the bottomof the casing 34, to rest on a supporting leg 36 made of suitabledielectric or isolating material. An example of coupling to theresonator by inductive coupling loops 35, which provide the input andthe output of the resonator, is shown in FIGS. 3 and 4.

The layer plate adjuster structure comprises a plurality of dielectricadjusting planes 37, 38, 39, 40 and 41, which are installedsubstantially concentrically and parallel one after another, themechanical engagement of said planes with each other and to theadjustment mechanism enabling movement of the adjustment plates 37-41both with respect to the resonator disc 33 and with respect to eachother, so that the adjustment plates 37-41 are arranged in layers on topof each other as the adjusting movement is proceeding.

In the embodiment described in greater detail in FIGS. 3 and 4, anadjusting mechanism, such as an adjustment screw 31 has been attached tothe top surface of an adjustment plate 37 which is most remote above aresonator disc 33. Each following lower adjustment plate 38-41 issuspended from the bottom surface of a corresponding previous adjustmentplate 37-40 by a spring means 42, which in free suspension keeps theadjustment plates 37-41 apart from each other. FIG. 3 shows a situationin which the layer plate adjuster is in its highest extreme position,and the adjustment plates 37-41 are hanging freely apart both from eachother and from the top surface of the resonator disc 33.

The adjusting mechanism 31 is arranged to move the adjustment plates37-41 in the perpendicular direction with respect to the top surface ofthe resonator disc 33. Thus, in an adjusting movement which is directeddownwards, upon the lowest adjustment plate 41 contacting the topsurface of the resonator disc 33, the adjustment plates start to movewith respect to each other against the force of the spring means 42between them, as the adjusting movement is proceeding, said adjustmentplates forming layers on top of each other on the resonator disc 33,starting from the lowest adjustment plates. FIG. 4 shows a situation inwhich the lowest adjustment plates 41, 40 and 39 are layered on top ofthe resonator disc 33 forming a substantially integral object with it.In the other extreme position of the adjusting movement, all theadjustment plates 37-41 are arranged in layers on the resonator disc 33.

In an adjusting movement which is directed upwards, the adjustmentmechanism 31 moves the highest adjustment plate 37, whereby theadjustment plates 37-41, layered on top of each other in an upwarddirection, start to become detached from each other actuated by thespring means 42, starting from the highest adjustment plates, until thesituation shown in FIG. 3 is finally reached.

By means of the layer plate structure of the invention, an adjustmentcurve in accordance with curve A in FIG. 5 is achieved as a function ofthe adjusting distance L=L1-L0. The highest frequency is achieved whenL=0, i.e. in the position in accordance with FIG. 3. The lowestfrequency is achieved when all the adjustment plates 37-41 are arrangedin layers on the resonator disc. Between points 50 and 51 of theadjustment curve, the lowest adjustment plate 41 approaches theresonator disc 33 until it contacts it at point 51. Thereafter, upon theadjusting movement proceeding downwards, the same happens againalternately to the following adjustment plates at points 52, 53, 54 and55. Thus, a relatively linear frequency adjustment and a long adjustmentdistance are achieved. The linearity may be increased by reducing thesize or the thickness of the adjustment plates, and the adjustingdistance may be lengthened by increasing the number of the adjustmentplates.

The figures and the explanation associated therewith are only intendedto illustrate the above invention. The resonator of the invention mayvary in its details within the scope of the attached claims.

I claim:
 1. A dielectric resonator, comprisinga dielectric resonatordisc, an electrically conductive casing, a plurality of dielectricadjustment plates which are installed concentrically and parallel witheach other and said dielectric resonator disc, a mechanical engagementbetween said dielectric adjustment plates enabling movement of saidadjustment plates in relation to each other and said dielectricresonator disc, an adjustment mechanism for moving said dielectricadjustment plates in a direction perpendicular to the dielectricresonator disc, for adjusting the resonance frequency of the dielectricresonator, the adjustment plates being arranged to be gradually stackedon said dielectric resonator disc during an adjusting movement towardssaid dielectric resonator disc, and said adjustment plates beingarranged to be gradually unstacked from said dielectric resonator discduring an adjusting movement away from said dielectric resonator disc.2. A dielectric resonator, comprisinga dielectric resonator disc, anelectrically conductive casing, a plurality of dielectric adjustmentplates which are installed concentrically and parallel with each otherand said resonator disc, an adjustment mechanism connected to the one ofsaid adjustment plates which is the most remote one above the resonatordisc, for moving said dielectric adjustment plates in a directionperpendicular to the resonator, for adjusting the resonance frequency ofthe dielectric resonator, a spring mechanism for suspending each of thefollowing ones of said dielectric adjustment plates from the respectiveprevious one of said dielectric adjustment plates, said spring mechanismbeing arranged to keep said dielectric adjustment plates apart from eachother in a free suspension, and the adjustment mechanism being arrangedto act against the spring mechanism for gradually stacking thedielectric adjustment plates on said resonator disc during an adjustingmovement towards said resonator disc.
 3. A dielectric resonatorcomprisinga dielectric resonator disc, an electrically conductivecasing, a plurality of dielectric adjustment plates, which are installedsubstantially concentrically and parallel one after another andsubstantially parallel with the resonator disc, an adjustment mechanismfor moving said dielectric adjustment plates in a directionperpendicular to the resonator disc, for adjusting the resonancefrequency, the mechanical engagement of said plates with each other andwith the adjustment mechanism enabling movement of the adjustment platesboth with respect to the resonator disc and with respect to each other,so that the adjustment plates are arranged in layers on top of eachother as the adjusting movement is proceeding, spring means, saidmechanical engagement comprising that the adjustment mechanism isconnected to the adjustment plate most remote above the resonator disc,and that each following one of the adjustment plates being suspendedfrom the bottom surface of the respective previous one of saidadjustment plates by said spring means, which in free suspension keepsthe adjustment plates apart from each other.
 4. A resonator as claimedin claim 3, wherein the adjustment mechanism is arranged to move theadjustment plates in the direction perpendicular to the top surface ofthe resonator disc, so that in an adjusting movement which is directeddownwards, upon a lowest one of said adjustment plates contacting thetop surface of the resonator disc, the adjustment plates start to movewith respect to each other against the force of said spring means, asthe adjusting movement is proceeding, said adjustment plates forminglayers on top of each other on the resonator disc, starting from thelowest one of said adjustment plates, and whereinin an adjustingmovement which is directed upwards, the adjustment plates layered on topof each other start to become detached from each other actuated by saidspring means starting from said most remote adjustment plate.